Decorative laminate sheeting is commonly used as the surface material for a wide variety of residential and commercial uses. For example, Andersson et al., in U.S. Pat. No. 4,362,778, taught foam laminates containing thermoplastic microspheres, usable as pin-attachable notice boards; Prince, in U.S. Pat. No. 3,908,059, taught decorative ceiling tile sheeting, having a core, and a patterned layer of expanded plastic particles; and Brooker et al., in U.S. Pat. No. 4,543,290, taught chemical resistant, high pressure laminate sheeting having a consolidated bottom core, melamine impregnated decorative sheet and top surface coating of vinyl ester terminated bisphenol A epoxy resin.
The Booker et al. laminate helped solve a major deficiency in decorative laminates, i.e., resistance to strong chemicals such as acids, bases, oxidizing agents, and solvents, and allowed use of decorative laminates in industrial laboratories and in hospital environments. The main requirement of chemical resistant decorative laminates is that the laminates have a thick layer of chemical resistant resin on the surface. In order to retain a thick layer of resin on the surface of laminates molded at about 1000 psi., it is essential that the surface have a low degree of flow during the molding process. Low flow in top coating resins can, however, cause mottling, resin streaks, and voids in finished laminates. Air can also be trapped in top thick resin layers, causing pits and other surface defects.
Brooker et al. used a 400 cps. to 800 cps. viscosity epoxy resin as a surface coating, and taught a wide variety of optional thixotroping agent additives, such as fumed silica, to help control flow properties of their top epoxy surface coating. However, even small amounts of such additives, when used, were noticeable at the laminate surfaces, especially at the surface of black colored laminates, and detracted from overall appearance of the laminate. What is needed is a more flow controllable surface resin for chemical resistant laminates. The surface resin should allow a thicker final coating after high pressure lamination without impairment of surface appearance, and the ability to resist highly corrosive chemicals.